1. Field of the Invention
The invention relates to optical communication equipment and, more specifically, to micro-electromechanical devices for use in such equipment.
2. Description of the Related Art
Optical communication equipment often employs micro-electromechanical systems (MEMS). A typical MEMS system may include an array of micro-machined mirrors, each mirror individually movable in response to an electrical signal. Such an array may be employed in an optical cross-connect, in which each mirror in the array receives a beam of light, for example, from an input optical fiber. The beam is reflected from the mirror and can be redirected to a different location, e.g., at which is located an output optical fiber. The particular output fiber may be selected by rotating the mirror. For better reflectivity, the mirror is typically coated with a thin layer of metal, e.g., gold or aluminum. More details on the principle of operation and methods of manufacture of MEMS devices including mirror arrays may be found, for example, in commonly assigned U.S. Pat. No. 6,201,631, the teachings of which are incorporated herein by reference.
One problem with prior art MEMS devices having metal-coated mirrors is thermo-induced bowing. More specifically, the mirror often becomes deformed, e.g., curled up, due to a mismatch in thermal expansion characteristics of the metal layer and the underlying substrate (typically silicon). This behavior may cause optical aberration and result in undesirable attenuation or even complete loss of the communication signal.